A memory system often includes semiconductor memory devices, such as dynamic random access memory (DRAM), synchronous DRAM (SDRAM), double data rate (DDR, DDR2, DDR3, etc.) SDRAM, etc. Various source devices, such as processors, peripheral devices (e.g., input/output devices), audio and video devices, may generate memory operation commands, including read memory operations to transfer data from memory devices to the source devices and write memory operations to transfer data from the source devices to the memory devices. Usually, a memory controller is implemented to receive the memory operation commands from the source devices and to control the memory devices to perform memory operations in response to the commands. The memory controller often includes command queues to capture the memory operation commands.
Priority parameters (e.g., Quality of Service (QoS) parameters) of the memory operation commands may be transmitted as parts of the commands to the memory controller. The memory controller may arbitrate among memory operation commands from different command queues and schedule execution of such commands based on their respective priority parameters. FIG. 1 illustrates an example of a memory controller scheduling execution of memory operation commands. An arbiter component 108 in a memory controller 100 schedules execution of memory operation commands 104 from multiple command queues 102 based on priority parameters 106 of the memory operation commands 104. As shown in FIG. 1, the memory controller 100 includes multiple system interface ports (SIPs) 110 which correspond to multiple command queues 102 respectively. A command queue stores one or more memory operation commands 104 which each include a priority parameter 106 (e.g., QoS). Each command queue has a current command which is at the top of the command queue and thus first in line to be serviced. The arbiter component 108 compares the priority parameters (e.g., QoS) of the current commands in different command queues, and selects one current command with a highest priority parameter to be serviced. For example, a command queue often operates in a first-in-first-out (FIFO) manner. That is, a current command of a command queue is the one that is received earlier than other commands in the command queue.